Rotary offset printing machines in which a plate cylinder together with a rubber blanket cylinder forms a printing couple are well known. It has been found that at high speeds of rotary printing machines--which may print on an elongated web or on sheets--cylinders tend to oscillate or otherwise not run exactly as intended, and the result of oscillation or otherwise differential behavior of the cylinders during printing results in printed copy which should be improved. Striations, stripings, differential inking and the like may be noticed. Printing machine cylinders, particularly blanket cylinders and plate cylinders, are excited to oscillate especially when the grooves in the cylinders in which the plates and the blankets are clamped run off against each other. Additional oscillations can be derived due to the drive gearing, that is, when meshing gears change from engagement of flanks of the gear teeth. Driven inkers and dampers, likewise subject to change in engagement of the flanks of the gear teeth, also may contribute to oscillatory behavior of printing cylinders. Many attempts have been made to prevent non-uniformity in printing, for example due to oscillation, see, for example, the following published patents:
Fed. Rep. Germany Pat. No. 26 13 688
Fed. Rep. Germany AS No. 11 93 516
Fed. Rep. Germany Pat. No. 11 93 516
German Dem. Republic (East Germany) Pat. No. 101,335
In spite of many and extensive attempts, it has not been possible to entirely eliminate the effects of non-uniform rotation on printed subject matter. The various proposals which have been made--see the referenced patents, for example--were intended to suppress oscillations by directly affecting the respective cylinder. It is, of course, always possible to very accurately balance each individual cylinder in a printing machine system and arrange the balance with respect to all other printing cylinders. This, however, is extremely expensive and, in mass production, while balancing of the individual cylinders as they are made is part of the manufacturing process, a re-balancing of individual cylinders in any system then would be necessary. Furthermore, the behavior of the cylinders at different speeds differs, so that balancing the cylinders for all speeds is not always possible. Within specific series of printing machines which are made, similar efforts are undertaken for all the machines to balance the cylinders and to avoid vibrations and oscillations. It is always possible, however, that a specific machine of a series differs in its oscillatory characteristics from all the other machines of the similar series. Individual correction and rebalancing of such a machine is very difficult and costly.
Various types of printing machines use rubber blanket cylinders which have a diameter larger than the diameter of the associated plate cylinder, for example twice the diameter. In such a machine, the plate cylinder revolves twice for each revolution of the rubber blanket cylinder, so that the rubber blanket cylinder will have two identical printed image information offset thereon. It has been found that there may be qualitative differences between the printed image transferred from such a rubber blanket cylinder which, for example, may be a difference in intensity or inking of a printed image transferred from one half of the rubber cylinder with respect to the adjacent half of the rubber cylinder, resulting from the second roll-off of the plate cylinder thereagainst.
It is known to provide rubber blankets, stretched on rubber blanket cylinders, with underlays, or underblankets.